1. Field of the Invention
The invention relates in general to a projection device and a controlling method, and more particularly to a scan projection device and a scan controlling method.
2. Description of the Related Art
Conventional projection technology uses pixel array for projecting an image. Along with the advance in projection technology, a new projection device which projects an image by way of scanning has been provided. The scan projection device uses a micro-electro-mechanical system (MEMS) mirror swinging in two dimensions to drive the image beam to scan a projection surface by way of such as raster scanning or Lissajous scanning, and produces an image through the persistence of vision perceived by human eyes.
In general, the MEMS mirror swings in two dimensional directions, such as a horizontal direction and a vertical direction. The swing frequency is defined as the resonance frequency of the MEMS mirror. For example, the horizontal swing frequency is 18 KHz, and the vertical scanning frequency is 60 Hz. Normally, the vertical resonance frequency of the MEMS mirror is about 10 Hz to 1000 Hz. That is, unless the inputted control signal is a precise mono frequency wave such as a 60 Hz sine wave, otherwise all harmonic waves of the vertical control signal whose frequency ranging between 10 Hz to 1000 Hz will make the MEMS mirror generate a corresponding reaction. Consequently, the MEMS mirror will have non-uniform speed in the vertical direction and horizontal bright lines will occur to the projection image.
To resolve the above problems, the industries currently suppress the phenomenon of horizontal bright lines by way of feedback control, which requires many additional controlling circuits, not only increasing cost but also decreasing reliability.